The present invention relates to a dry toner for developing latent electrostatic images used in electrophotography, electrostatic recording, and electrostatic printing, and particularly to a toner with improved resistance to toner staining of vinyl chloride products.
As conventional technology for improving the toner staining on vinyl chloride products, in Japanese Laid-Open Patent Application No. 59-162564 there is disclosed the use of a homopolymer or copolymer of (meta)acrylic ester having an alkyl group with three or less carbon atoms, or a copolymer of styrene and (meta)acrylic ester (styrene monomer units 30 wt.% or less). However, when acrylic ester is used, if the amount of styrene is 30 wt.% or less, the glass transition temperature (Tg) of the copolymer is low and the toner will probably cake during storage. When methacrylic ester is used, because the Tg is high, the storage characteristics of the toner are good, but it has a drawback inasmuch as it is impossible to obtain adequate image fixing performance.
In addition, in Japanese Laid-Open Patent Application No. 59-166965, there is disclosed the use of a polymer containing 20 wt.% to 50 wt.% of at least one compound selected from the group consisting of hydroxyalkyl methacrylate, hydroxyalkyl acrylate, methacrylic acid, acrylic acid, glycidyl methacrylate, glycidyl acrylate, methacrylonitrile, and acrylonitrile, with a glass transition temperature of 50.degree. to 80.degree. C. By the introduction of a polar group into a binder resin, the resistance to toner staining of vinyl chloride products is improved, but there is some water absorption so that the electrostatic charge environmental stability becomes unsatisfactory.
There is generally an improvement in the resistance to toner staining of vinyl chloride products as a result of the extremely high increase in the crosslinking density of the binder resin, but the image fixing performance becomes unsatisfactory. In addition, resins with a solubility parameter which is far from that of a vinyl chloride plasticizer will be acceptable, but there are various inconveniences. For example, polyester has a strongly negative polarity which makes it difficult to use with a positive toner.